<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .ff {
            font-weight: 100;
        }

        div {
            /* 
            默认：normal =400
            加粗：700=800=900=bold
            减小加粗：100=200=300
            */
            /* 700=800=900=bold */
            font-weight: 700;
        }

        .first {
            font-weight: bold;
        }
    </style>
</head>

<body>
    <p class="ff">
        设置字体加粗
    </p>
    <div>
        设置字体加粗div
    </div>

    <p>
        <span class="first">新闻</span>
        <span>军事</span>
        <span>国内</span>
        <span>国际</span>
    </p>
</body>

</html>